The subject matter of the present invention relates generally to oscilloscope sweep systems, and in particular to a dual time-base sweep system for accurate differential time measurements down to and including zero time, defined herein as the time base triggering event.
Conventional dual time base oscilloscopes have two sweep generators in which the starting point of a so-called delayed, or B, sweep may be selected at any time point along a so-called delaying, or A, sweep to permit expanding selected A sweep segments or making differential time measurements between certain events. It is imperative in oscillography that the time base sweep signal be linear so that the trace-producing spot is driven across the screen of the cathode-ray tube (CRT) at a constant rate of speed. For the most part, modern oscilloscopes have very linear sweeps over a specified region which excludes a short period of time following sweep initiation. The reason for this is, of course, that sweep start up immediately following sweep initiation is non-linear due to the inherent bandwidth and non-linearity of the devices of the sweep system at turn on. This nonlinear sweep startup precludes accurate differential time measurements beginning with the A-sweep triggering event because the nonlinear startup portion is necessarily included in the measurement when the delay reference is set at zero. Moreover, in most cases, the triggering event is not even visible on the delayed sweep because of the inherent delays in the A and B sweeps.
Another problem in prior art oscilloscopes is that the displayed sweep trace is shifted to the right at higher sweep speeds because the unblanking pulse must be delayed to hide the non-linear sweep startup.